Structure–properties relationship in RE3−Mg Ni9H10–13 (RE = La,Pr,Nd) hydrides for energy storage

Abstract

Ternary RE 3-x Mg x Ni 9 intermetallics are promising battery electrode materials. Studies of the structure-properties relationships in the (La,Pr,Nd) 3-x Mg x Ni 9 H 10-13 hydrides and initial intermetallics revealed the following: a) Increase of magnesium content causes a gradual shrinking of the trigonal unit cells (a, c, V) for all studied RE metals, with the highest solubility range of Mg reached in REMg 2 Ni 9 ; b) Significant lowering of the thermodynamic stability follows an increase in magnesium content from x =1.0 to 1.1-1.2 and a replacement of La by Pr and Nd, with desorption pressures changing in a broad range, from 0.01 bar to 20 bar H 2 ; c) Neutron powder diffraction shows a nearly equal distribution of D atoms within the REMgNi 4 and RENi 5 layers; d) Local hydrogen ordering occurs within the H-sublattice built from MgH 6 octahedra and NiH 4 tetrahedra displaying a directional metal-hydrogen bonding. A partial substitution of Mg for RE allows the electrochemical discharge capacity of the (La,Pr,Nd) 3-x Mg x Ni 9 hydrides to become 25% greater than that of the commercial AB 5 -type electrodes, reaching 400 mAh/g. Synthesis of the materials with a high degree of homogeneity is important and has been achieved by choosing an appropriate synthesis route, content of Mg in the initial mixtures, and time and temperature of the homogenisation process.

Study on solid solubility of Mg in Pr 3−x Mg x Ni 9 and electrochemical properties of PuNi 3 -type single-phase RE–Mg–Ni (RE = La, Pr, Nd) hydrogen storage alloys

“…8(a), La 2 MgNi 9 alloy possesses the maximum hydrogen storage capacity of 1.56 wt.%, and Pr 2 MgNi 9 and Nd 2 MgNi 9 alloys follow with 1.50 and 1.48 wt.%. Similar results also can be observed in the report by Yartys et al [13]. The midpoint plateau pressure in desorption process for the three alloys are 0.004, 0.020 and 0.017 MPa, respectively.…”

“…This is because the atom radius atom of La (0.1877 nm) is larger than Pr (0.1828 nm) and Nd (0.1821 nm), contributing to a lager cell volume. The lattice parameter results are in good agreement with the recent reference data [13].…”

“…Yartys et al found that RE 2 MgNi 9 -H 2 have a significantly lower thermodynamic stability as compared to La 2 MgNi 9 -H 2 , with the hydrogen desorption pressure increasing from 0.1 bar for La 2 MgNi 9 -H 2 to 20 bar for RE 2 MgNi 9 -H 2 [13]. Studies on annealed Nd 0.88 Mg 0.12 Ni 3.10+x Al 0.20 (x = 0.0, 0.1, 0.2, 0.3) alloys showed that the stoichiometry of AB 3.5 alloy showed the best charge retention and cycling stability [14].…”

Phase equilibria in the Tb-Mg-Co system at 500°C, crystal structure and hydrogenation properties of selected compounds

“…type PuNi 3 ) with the substitution of Tb by Mg in 6c site only. Tb 2 MgCo 9 is isostructural to R 2 MgNi 9 (R = La, Nd, Pr) [15][16][17].…”

LaNi5-Assisted Hydrogenation of MgNi2 in the Hybrid Structures of La1.09Mg1.91Ni9D9.5 and La0.91Mg2.09Ni9D9.4

“…Interestingly, a substantial contraction takes place not only for the (La,Mg)2Ni4 slabs, but also for Mg-free CaCu5-type LaNi5 slabs. Hydrogen interaction with the La3−xMgxNi9 alloys has been investigated by in situ synchrotron X-ray, neutron powder diffraction, theoretical modeling, electrochemical studies as metal hydride battery anode materials, rapid solidification and pressure-composition-temperature studies [1,2,[5][6][7][8][9][10]. In the whole substitution range, La3−xMgxNi9 alloys form intermetallic hydrides with H/M ratios ranging from 0.77 to 1.16.…”